28 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Arranged geologically the distribution is as follows : 



Of all of the Paleozoic Stelleroidea (174 species), not a single one 

 is common to North America and Europe. Of genera havmg specific 

 representation in more than one continent there are the foUo^yklg: 

 Hudsonaster, 5 in America, 1 in Scotland; Mesopalseaster, 13 (7 doubt- 

 ful) in America, 1 in England, ? 1 in Germany; Petraster, 3 in America 

 (1 doubtful), 1 m Australia; Stenaster, 1 m America, ? 1 in Ireland and 

 Wales, ? 1 in England, ? 1 in Eussia; Vrasterella, 5 in America, 1 in 

 Scotland, ? 1 in Wales, ? 1 in France, 2 in England, 1 in Australia, 

 1 in Germany, 1 in Russia; Palseosolaster, 1 in Germany, ? 1 in 

 America; Protaster, ? 2 in America, 1 in England, 2 (1 doubtful) in 

 Wales; Tremataster, 1 m America, ? 1 in Belgium. Of Ophiuroidea, 

 none have wide distribution. 



Nearly all of the species have very short geologic ranges, but very 

 few occurring m more than a single formation. 2Iesopalxaster 

 intermedins ranges from the ? Utica to the Maysvillian, M. sliafferi 

 from the Maysvillian to the Richmondian, Alepidaster Jlexuosus irom. 

 the basal Edenian to the upper Maysvillian, Hudsonaster incomp- 

 tus from the Edenian into the Richmondian, Promoimlxaster mag- 

 nificus and Petraster spedosus from the Maysvillian to the Rich- 

 mondian. 



These tables also show that the Ophiuroidea do not begin earlier 

 than the Lower Carboniferous (Burlington) and that the Auluroidea 

 cease to exist after the same period, for none are as yet known in the 

 Upper Carboniferous or Permic. The latter attained their maximum 

 of development in the Siluric and Devonie, with very rapid decline 

 in the Lower Carboniferous. 



The great development of Asteroidea in the Ordovicic is due to the 

 marked specific evolution of the genera Mesopalseaster and Promo- 

 palseaster in North America. This knowledge is the result of care- 

 ful work by local collectors in areas abounding in good fossils. On 

 the other hand the marked rise in specific representation in the De- 

 vonie is due to the protracted collecting in the earher beds of this 

 period, the roofing slates of Bundenbach, Germany. 



Preservation and occurrence. — Starfishes are most often preserved 

 in sandstones and mudstones and least often in limestones. The 



